(1) Field of the Invention
This invention relates to providing a constant voltage power source in a vehicle.
(2) Prior Art
During recent years, there has been an increasing use of various electronic components in motor vehicles. For example, electronics is used in instrumentation which displays information such as time, speed, fuel level, and other information desired by the vehicle operator. Various other electronic vehicle controls include modules for governing the operation of vehicle occupant restraints, voltage regulators and low tire pressure sensors. There is also increasing use of electronics in entertainment and automotive communication equipment such as radios, tape players and citizen band transmitter/receivers. Electronics has also been incorporated into powertrain components which affect the ability of the car to start and to continue to run. For example, there are electronic components for alternators, distributors, speed control, ignition and engine emission controls.
Although use of electronic components in motor vehicles has many advantages, improper operation of such electronic components can severely affect the ability of the motor vehicle to function. For example, improper operation can be due to excessive variation in supply voltage which can occur during prolonged cranking of the starter motor during cold weather. There is a great current drain on the main vehicle battery which causes the voltage of the main battery to drop substantially and can result in inoperability of some electronic components. If these electronic components govern the ignition of the motor vehicle engine, the motor vehicle may remain inoperable.
The prior art teaches the use of reverse bias diodes in conjunction with the charging of a battery. For example, U.S. Pat. No. 3,921,049 issued on Nov. 18, 1975 to Mellors et al discloses a charging circuit for battery operated devices powered by solar cells. Further, U.S. Pat. No. 4,004,208 issued on Jan. 18, 1977 to Tamminen discloses a starting aid and reserve light for a vehicle wherein the starting aid includes a secondary battery which can be connected, in addition to the starter battery, to the starter motor. U.S. Pat. No. 3,463,995 issued to Herold on Aug. 26, 1969 teaches powering a starter motor by a main battery alone or by the main battery and a complementary battery in parallel. None of the aforementioned patents teach or suggest an integral electrical supply apparatus for powering motor vehicle electronic components requiring a constant voltage in situations when the voltage of the main battery has dropped to an undesirably low level. These are some of the problems this invention overcomes.